Click the Start button Picture of the Start button, right-click Computer, and then click Properties.
If "64-bit Operating System" is listed next to System type, you’re running the 64-bit version of Windows Vista or Windows 7.
If "32-bit Operating System" is listed next to System type, you’re running the 32-bit version of Windows Vista or Windows 7.
The edition of Windows Vista or Windows 7 you're running is displayed under Windows edition near the top of the window.